Passive Infrared Sensor (PIR): These are the most common type. Passive infrared sensors are triggered when a combination of heat and movement is detected in the monitored zone. This means a car, truck, person, or any animal will trigger the sensor IF it passes through the monitored zone.
Magnetometer Bases Sensor: These sensors are designed to pick up automobiles only and they work when heavy metallic objects are detected in the monitored zone. The sensor typically has a probe that is buried just under the driveway or parallel to the driveway. When a car or truck drives through the zone, the probe detects the change in the magnetic field and triggers.
Pneumatic: Do you remember the old gas stations that had a rubber hose stretched across the entrance? It would ring a bell as the car rolled over the hose. This type of sensor is called a pneumatic sensor. When a heavy car rolls over the hose, the change in air pressure inside the hose triggers the sensor.
Break Beam Sensor: These sensors work in a pair and when someone or something passes between the pair of the sensor, they detect that the beam between them was broken and are thus, triggered.